Continuous casting with circular trough mold

ABSTRACT

A generally horizontal annular trough forming a circular mold cavity is rotated about a generally vertical axis to transfer molten metal from a feeding station through a solidifying zone and thence through a discharge station where the solidified metal is continuously removed from the mold. The solidifying zone is formed by a cooling station including means for continuously cooling the trough to solidify molten metal in the mold, and a hood overlying at least part of the cooling station forms a substantially enclosed space above the open top of the mold. This space contains nozzle means for concentrating on the upper surface of the metal a stream of nonoxidizing gas which, prior to complete solidification of the metal, forms a solidified skin across its upper surface to prevent escape of gas from within the metal. Thus, when the metal is of the type that evolves gas to offset shrinkage during solidification, the upper surface of the solidified casting is flat rather than concave.

United States Patent [72] lnventor Douglas C. Yearley Westfield, NJ. [21 Appl. No. 647,680 [22] Filed June 21,1967 [45] Patented Sept. 7, 1971 [73] Assignee Phelps Dodge Copper Products Corporation New York, N.Y.

[54] CONTINUOUS CASTING WITH CIRCULAR TROUGl-l MOLD 6 Claims, 4 Drawing Figs.

[52] US. Cl 164/283, 164/87, 164/276 [51] Int. Cl B2241 11/12 [50] Field of Search 164/72, 87, 89, 259, 117, 273, 268, 276, 278,73, 156, 155, 281, 66, 277,128, 283, 297, 90, 278

[56] References Cited UNITED STATES PATENTS 3,284,859 1 111966 Conlon et a1. 164/259 2,099,208 1 H1937 l'lorsfall et al. 164/259 Assistant Examiner-John S. Brown Attorney-Davis, Hoxie, Faithfull & l-Ilapgood 1 ABSTRACT: A generally horizontal annular trough forming a circular mold cavity is rotated about a generally vertical axis to transfer molten metal from a feeding station through a solidifying zone and thence through a discharge station where the solidified metal is continuously removed from the mold. The solidifying zone is formed by a cooling station including means for continuously cooling the trough to solidify molten metal in the mold, and a hood overlying at least part of the cooling station forms a substantially enclosed space above the open top of the mold. This space contains nozzle means for concentrating on the upper surface of the metal a stream of nonoxidizing gas which, prior to complete solidification of the metal, forms a solidified skin across its upper surface to prevent escape of gas from within the metal. Thus, when the metal is of the type that evolves gas to offset shrinkage during solidification, the upper surface of the solidified casting is flat rather than concave.

a! E F4 PATENTEUSEP mu 3503 37 sum 1 OF 3 INVENTOR.

I N VENTOR.

PATENTEH SEP 7 I971 sum 2 or 3 CONTINUOUS CASTING WITH CIRCULAR TROUGII MOLD This invention relates to casting with apparatus of the type in which the molten metal is continuously fed from a supply station into a mold consisting essentially of a circular trough rotating about a generally vertical axis of the circle, whereby the metal solidifies as it is carried by the rotating trough to a discharge station which removes the metal continuously as a rod, or the like.

An apparatus of the above-mentioned type affords numerous advantages, particularly in the improved form disclosed in U.S. Pat. No. 3,284,859 granted Nov. 15, i966. In the apparatus disclosed in said patent, the metal is solidified in a cooling zone or station through which the mold rotates, and an overlaying hood forms a substantially enclosed space in which a protective atmosphere of nonoxidizing gas is maintained to minimize absorption of oxygen by the solidifying metal. However, this manner of solidification leaves much to be desired when the metal is of the type in which gas evolution during solidification can be controlled to offset shrinkage. More particularly, with that type of metal the solidification results in a concave surface on the top of the discharged casting, making it quite unsuitable for hot rolling.

The principal object of the present invention is to provide a continuous casting method and apparatus of the character described in which the upper surface of the discharged casting is flat, so that the casting is well adapted for hot rolling.

The method of the present invention is concerned with metals (including metal alloys) of the type adapted to generate a controlled quantity of gas during solidification to offset the solidification shrinkage, for example, oxygen-bearing copper commonly known as tough pitch copper. I have found that in casting such metals with the aforesaid prior apparatus, the enclosed protective atmosphere overlying the rotating mold prevents convective cooling of the top surface of the metal so that solidification proceeds from the bottom toward the top, and all the evolved gas passes through the mol ten metal pool into the atmosphere, the resulting shrinkage causing the undesired concave shape of the upper surface of the casting.

According to the invention, the substantially enclosed space within the hood at the cooling zone contains nozzle means connected to a source of pressurized nonoxidizing gas, and the nozzle means are disposed to concentrate a stream of the gas upon the upper surface of the molten metal in the rotating mold. The nozzle means are so dimensioned and located as to direct the gas stream at a flow rate and position to form, by convective cooling, a solidified skin across this upper surface which entraps the gas bubbles evolved as solidification of the underlying metal proceeds. The gas bubbles thus entrappedform discrete pours within the casting predominately near its upper surface, the volume of these pours serving to offset solidifying shrinkage so that the desired flat upper surface of the casting is obtained.

For best results, the nozzle means include at least one nozzle directed toward the feeding station; and the hood has an outlet located between the nozzle and feeding station and to which the stream passes countercurrently to the movement of molten metal by the rotating mold.

The invention is described in more detail hereinafter with reference to the accompanying drawings, in which:

FIG. l is a plan view of a preferred form of the new apparatus;

FIG. 2 is a side elevational view, partly in section, of the apparatus illustrated in FIG. 1, showing details of the moltenmetal feeding means and part of the hood overlying the coolmg zone;

FIG. 3 is a view similar to FIG. 2 but showing a different portion of the hood and the nozzle means therein; and

FIG. 4 is a sectional view on the line 4-4 in FIG. 3.

Referring to FIG. 1, the continuous casting apparatus there shown comprises a stationary vertical post or axle extending through a hub 21 having a close-rotating fit on the axle. Hub 2| is adapted to be rotated on the axle at constant speed by a motor 22 connected through a variable speed transmission 23 and shaft 24 to a hovel gear 25 meshing with u huge bevel gear 26, the latter being secured to hub 21.

The hub 2! has rotating spokes 28 secured at their outer ends, as by welding, to an annular trough 29 having a circular mold cavity 29a which is open at the top. The ring shaped trough 29 is supported on horizontal rollers30 spaced around the vertical axle 20 and mounted on suitable stationary supports (not shown).

The motor 22 operates through hub 21 and spokes 28 to rotate the annular trough 29 about the vertical axle 20 as an axis. For simplicity and to avoid duplication, only some of the rollers 30 are illustrated, it being understood that they are provided in sufficient number to support the circular trough 29 in a horizontal position when it is rotated and loaded with the casting metal.

The molten metal is fed continuously into the rotating mold cavity 29a by feeding means shown generally at 32 in FIG. 1. The mold rotates counterclockwise as viewed in FIG. 1, thereby carrying the metal from the feeding means 32 through an overlying gas-applying station 33 where the metal is subjected on its exposed upper surface to a nonoxidizing gas while being cooled by water sprayed against the outside of the trough 29 from stationary nozzles 65 spaced along the trough. These nozzles fonn a cooling station or zone and are continuously supplied with cooling water from a supply source (not shown) through tubes 66, the spent cooling water descending from the trough being collected in any suitable manner. Continued rotation of the mold carries the solidified metal to a cast-metal discharge station 34, where it is continuously discharged from the mold. As the mold continues to rotate from discharge station 34, it may pass through stations (not shown) for preheating and dressing the mold before it reaches the feeding means 32. The details of the discharge station 34 and the preheating and dressing stations may be as disclosed in the aforementioned US. Pat. No. 3,284,859.

Referring now to FIG. 2, the feeding means 32 comprise a pouring cup 36 preferably having a lining of refractory material. The cup 36 forms a main chamber 37 open at the top for receiving molten metal from a launder 38 or other source. The pouring cup also has an overflow weir 39 over which the main chamber 37 communicates with a discharge spout 40 of the cup. The spout 40 has an entrance 40a which receives the molten metal from the overflow weir 39 by way of a subchamber 37a of the cup. From its entrance end 40a, the spout extends downwardly and forwardly in the direction of rotation of the underlying mold cavity 29a, the spout terminating outside the body of the cup 36 in a discharge end 40b. The latter is received in the upper part of the mold cavity 29a with a slight clearance at each side of the discharge end, and the throughflow area of the discharge end has a width substantially equal to the width of the mold cavity 29a.

The pouring cup 36 is supported by means comprising a pair of graphite shoes 42 and 43 seated on. the bottom of the mold cavity 29a and each having a sliding fit in this cavity. The shoes are secured to the bottom of cup 36, by means including bolts 42a and 4311, respectively, for connecting the shoes to depending flanges 36a of the cup. The front shoe 42 is located adjacent the discharge end 40b of the spout and has a close sliding fit in the mold cavity 29a so as to form a dam for preventing reverse flow of the molten metal entering the cavity from the spout 40. The shoe means 42-43 thus floatingly support the pouring cup 36, including its spout 40, to allow free movements thereof vertically and laterally as the trough 29 rotates. An element 45, serves to restrain the cup 36 against rotation with the trough 29. This element, as shown, is a fixed stop engageable by the front. end of cup 36, thereby holding the cup against movement by rotation of the trough while allowing free movements of the cup vertically and laterally.

50 overlying the trough As shown in FIG. 2, the pouring cup 36 is located closely adjacent the gas-applying station 33, which comprises a hood 29 and held stationary by a suitable support 51 (FIG. 1). The hood 50 has depending sidewalls which lie closely adjacent opposing sidewalls of trough 29 (FIG. 4), whereby the hood forms a substantially enclosed space 50a above the mold cavity 290.

Within the hood space 50a is .a. manifold 53 extending lengthwise of themold cavity 294 and directly above it, as shown in FIGS. 3 and 4. The manifold is provided with nozzle means comprising-a plurality of depending nozzles 54 having their discharge ends located close to the upper surface of the metal in the mold. As shown, there are four such nozzles 54 spaced lengthwise of the underlying mold cavity and extending downwardly and rearwardlytoward the feeding station 32, so that the discharge upper surface of the metal countercurrently to the direction of its travel in the mold. I

The manifold 53 is secured to and supplied from the'lower end of a tube 55 extending through the top of hood 50, the

tube being mounted in a suitable fitting 56 on'the hood. Above the hood 50, tube 55 is provided with a valve 57 through which it isconnectedto a supply pipe 58 constituting a source of nonoxidizing gas under pressure. The gas supplied by source 58 is'preferably an inert gas, such as nitrogen or argon; and by means of the valve 57, the rate at which the gas is discharged from nozzles 54 may be adjusted.

As shown in FIG. 2, the top of hood 50 is provided with a view port covered by a sight glass 60. The latter is located near the pouring cup 36 to enable inspection of the molten metal as it is delivered into the mold from spout 40, which extends into g the rear end of the hood. Between the sight glass 60 and the pouring cup 36, the top of hood '50 is provided with an outlet port 61 for discharge of gas supplied by the nozzle means 54.

The nozzle means 54 are located a sufficient distance beyond the feeding spout 40 to allow the molten metal in the mold to quiesce before its upper'surface is subjected to the streams of nonoxidizing gas from the nozzles...l-lowever, the nozzle means 54 are so positioned in relation to the cooling means 65-66 that the interior of the body of molten metal has not solidified by the time its upper surface is subjected to the action of the jets from nozzles 54. The dimensions of the nozzle means 54 and the adjustment of valve 57 are such that the streams of nonoxidizing gas are concentrated upon the upper surface of the molten metal at a flow rate sufficient to solidify this upper surface prior to complete solidification of the metal in the mold. Thus, a solid, flat metal skin is formed at the upper surface of the metal by convection cooling; and solidification of the metal then proceeds from the bottom and sides as well as the top, with the result that the metal casting discharged at thestation 34 (FIG. 1) has a flat upper surface as well as being flat at the sides and bottom. Such a casting is well adapted for hot-rolling.

The above-mentioned convection cooling, under the conditions as described, has the effect of sealing the upper exposed surface of the incompletely solidified metal and thereby preventing escape of gas from the interior of the metal, which would cause the upper surface to take a concave form as solidification of the metal continues.

As an example of the location of the nozzle means 54 to attain the above described results, such means may be located about 2 feet beyond the feeding spout 40b when the circular mold cavity 29a has a diameter of feet. Also by way of example, the valve 57 may be adjusted to maintain a gas pressure from each nozzle is directed against the of about 10 pounds per square inch in the manifold 53.

It will be understood that the gas delivered from the nozzles 54 for the convection cooling heretofore described also maintains a nonoxidizing atmosphere in the hood space 50a, to

' prevent absorption of oxygen by the metal while it is solidifying. This atmosphere as a whole moves slowly in the direction countercurrent to the movement of the mold, that is, toward the gas outlet 61. While l prefer that the gas nozzles 54 be inclined as shown in FIG. 3, it is to be understood that they maybe directed straight downwardly or otherwise, provided that they concentrate their jets of gas upon the. upper surface.

of the rnetal in the mold so ast solidify that'surface by con} vectioncooling. I i

The 'teedingrneans 32'for thernolten metal, asshown gin- FIG. 2, are preferred but form no part of thepresent invention, such feeding means being the subject of an application of Kurt R. Behrsin filed concurrently herewith.

To illustrate the effect: of the present invention, tough pitch copper was continuously cast into a bar having a crosssectional area of 4 square inches, at a rate of 30 feet per minute. When the gas flow through the nozzle means 54 was interrupted, the upper surface of the casting promptly became concave; but when the gas flow was resumed, this cast surface returned to its flat or level shape. a

1 claim:

1. In combination with a generally horizontal annular trough forminga circular mold'ope'n at the top and adapted to receive molten metal, a feeding station adjacent the trough and including means for continuously feeding molten metal into said mold, means for rotating the trough about a generally vertical axis in one direction relative to the feeding station, and a discharge station adjacent the trough and including means for continuously removing solidified metal from the mold as the trough rotates, a cooling station through which the trough movesin rotating'from the feeding station, to the discharge station, continuously cooling the trough to solidify molten metal in said mold, a hood overlying at least part'of the cooling station and forming a substantially enclosed space above the mold, a source of pressurized nonoxidizing gas, and nozzle means in said space connected to said source and disposed to concentrate a convection-coolingstream of said gas upon the upper surface of the metal in said mold, said nozzle means being dimensioned and located to direct said stream at a flow rate and position to solidify said upper surface by convection cooling prior to complete solidification of the metal in the mold.

2. The combination according to claim 1, in which said nozzle means include a nozzle directed toward said feeding station.

3. The combination according to claim 1 in which said nozzle means include a plurality of nozzles spaced along the mold.

4. The combination according to claim 1, in which said nozzle means include a plurality of nozzles spaced along the mold, said nozzles being directed toward said feeding station.

5. The combination according to claim 1, comprising also a valve connecting the nozzle means to said source and adjustable to vary said flow rate of the gas.

6. The combination according to claim 1 in which said nozzle means include a nozzle directed toward said feeding station, the hood having an outlet located between said nozzle and the feeding station and to which said stream is directed countercurrently to movement of molten metal by the rotating mold. Y

said cooling station including means'fon 

1. In combination with a generally horizontal annular trough forming a circular mold open at the top and adapted to receive molten metal, a feeding station adjacent the trough and including means for continuously feeding molten metal into said mold, means for rotating the trough about a generally vertical axis in one direction relative to the feeding station, and a discharge station adjacent the trough and including means for continuously removing solidified metal from the mold as the trough rotates, a cooling station through which the trough moves in rotating from the feeding station to the discharge station, said cooling station including means for continuously cooling the trough to solidify molten metal in said mold, a hood overlying at least part of the cooling station and forming a substantially enclosed space above the mold, a source of prEssurized nonoxidizing gas, and nozzle means in said space connected to said source and disposed to concentrate a convection-cooling stream of said gas upon the upper surface of the metal in said mold, said nozzle means being dimensioned and located to direct said stream at a flow rate and position to solidify said upper surface by convection cooling prior to complete solidification of the metal in the mold.
 2. The combination according to claim 1, in which said nozzle means include a nozzle directed toward said feeding station.
 3. The combination according to claim 1, in which said nozzle means include a plurality of nozzles spaced along the mold.
 4. The combination according to claim 1, in which said nozzle means include a plurality of nozzles spaced along the mold, said nozzles being directed toward said feeding station.
 5. The combination according to claim 1, comprising also a valve connecting the nozzle means to said source and adjustable to vary said flow rate of the gas.
 6. The combination according to claim 1, in which said nozzle means include a nozzle directed toward said feeding station, the hood having an outlet located between said nozzle and the feeding station and to which said stream is directed countercurrently to movement of molten metal by the rotating mold. 